1. Field of the Invention
The invention relates generally to wafer handling and support systems and, more specifically, to wafer handling and support systems which do not use tape.
2. Description of the Background
Many different types of semiconductor processing systems require the use of wafer handling systems or wafer support systems. Wafers are comprised of a number of integrated circuits or "dice". Through a dicing process, the dice are cut from the wafer. Traditionally, the dicing process is performed with wafer spindle and blade assemblies having circular cutting blades. Such devices may be obtained commercially from Disco Hi Tec America, Inc., Santa Clara, Calif. The cutting blades are oftentimes nickel-plated with a diamond grit cutting edge to allow for smooth cuts with a minimum amount of splintering of the wafer itself.
It is well known in the art to place the wafers on a surface, known as a "cutting chuck", where the wafers are diced by a cutting blade. During the dicing process, the cutting blade may cut through the wafer and into the cutting chuck itself. That damages the cutting blade, accelerates blade wear, and necessitates premature blade replacement to insure that wafers are not damaged during dicing.
To avoid cutting into the chuck, tape is used to hold the wafer in place on the cutting chuck during the dicing process. It is well known in the prior art to use a wafer frame and adhesive tape to maintain dice in place during the dicing process. The wafer frame is generally flat and defines an opening which is larger than the wafer. The adhesive tape is attached to the wafer frame and stretched across the opening. A wafer is secured to the adhesive tape within the opening, and the frame is secured, for example by a vacuum, to the cutting chuck for dicing. After the dice have been cut, the frame, along with the adhesive tape and the dice, are removed from the cutting chuck. The dice are separated from the adhesive tape, the adhesive tape is removed from the frame, and the frame is reused. The adhesive tape is known as "sticky back" and is usually a polymer based film such as polyvinyl chloride ("PVC"), with an adhesive coating on one side. The adhesive tape is usually about 3 mils thick. The dice stick to the adhesive, so that when the wafer is cut the dice remain in place on the cutting chuck and are not scattered. Because a cutting blade extends slightly below the wafer, the cutting blade is exposed to the adhesive tape. The adhesive binds to the cutting blade, causing accelerated blade wear and "gumming up" of the cutting blade. A gummed-up cutting blade reduces the effectiveness of the cutting blade, increases friction between the cutting blade and the wafer, and increases the tendency of the cutting blade to bind and break. Heat is generated from friction between the cutting blade and both the wafer and the adhesive. The faster the cutting blade is moved through the wafer, the more heat is generated, and that heat is increased when the cutting blade is gummed-up. In addition, the risk of the cutting blade binding increases as the temperature of the cutting blade increases. Furthermore, the silicon substrate may be damaged by the heat. As a result, the heat generated by the dicing process, and all of the undesirable side effects of the heat, limits the rate at which the cutting blade can be moved across a wafer. As the rate of the dicing processes decreases, the amount of time required to dice a wafer increases.
The accelerated wear and damage caused to cutting blades from contact with the chuck and the adhesive requires that they be replaced after dicing only about five or six wafers. Worn cutting blades lack exposure of the diamond particles to cleanly cut a wafer. The continued use of a worn cutting blade may result in damaged or totally destroyed wafers caused by a cutting blade breaking and spraying debris across the wafer. Replacing cutting blades is expensive not only in terms of the costs of the cutting blade, but also in terms of down time of the dicing process and interruption of the fabrication process while an old cutting blade is being removed and a new cutting blade is being installed.
Efforts have been made to design systems which do not require the use of tape. One such system is disclosed in U.S. Pat. No. 5,803,797. That patent discloses a patterned chuck with vacuum holes through the chuck to hold the die in place both during and after dicing. The patterned chuck has a plurality of recesses in its surface to accommodate the cutting blade. However, this requires that a special chuck be used for each type and size of die to be cut, as the plurality of recesses on each patterned chuck correspond to the particular type and size of dice to be cut.
Therefore there exists a need for an improved wafer handling system which reduces the amount of wear and damage to the cutting blade while allowing for efficient cutting and that is both economical and time efficient. More specifically, there is a need for a cutting chuck and adherence system that does not interfere with the cutting blade during dicing, but that secures a wafer onto the chuck without the need for a tape adhesive while proving to be cost effective and adaptable for use with a variety of wafers.